A conventional digital measuring meter, for example, a taximeter, a gas filling meter, a weighing mechine or other such rental equipment with an automatic timing base, generally includes a sensor for detecting signals from a sensing element when performing measurement operation, and, a counter for receiving, counting and converting the sensed signals into fare or charge value displayed on the meter. As shown in prior art FIGS. 1 and 2, a conventional measuring meter M will receive the signals transmitted from the sensor S. A pulse signal of square wave is transmitted from an output terminal S1 of the sensor S through a transmission line T, to be received by an input terminal M1 of the measuring meter M. Even the sensor S and the meter M are respectively protected by well-sealed packing cases S2, M2, someone may install an external signal generator E on the transmission line T between the sensor S and the meter M trying to intentionally increase the signals to be received by the meter as additionally supplied by the generator E in order to illegally earn a dishonest fare or charge from the fraud meter.
The inventor has found such a fraud provoking defect in conventional digital measuring meters to be present, and has invented the present anti-fraud means to prevent the cheating of meter fares.